Description of column-types used to define regressions

REGRESSOR: regression value

It is possible to have in a data set one or several columns with column-type X. Within a given subject-occasion, string “.” will be interpolated (nearest neighbor interpolation is used) for dose-lines only (N.B.: if there is an EVID column dose-lines correspond to EVID = 1 or EVID = 4). Else wise, for measurement line, no interpolation is performed. If no regressor is defined on such a line, it will be replaced by a NaN. Therefore, in the following data set example,